can 15 year olds be allowed to voleneier as chefs in a non profit kitchen

Sorry about the spelling. My computer auto corrected without me realising.
I'm not really getting the answers to the question I thought I was asking so I shall clarify.
I'm looking to see if I can set up a 'school cafe' on site only staffed with student volunteers.
And I want to make sure it's legal before I put the idea forward.

can 15 year olds be allowed to voleneier as chefs in a non profit kitchen

In a kitchen..probably not. I reckon you'd have to be 16. I had to be 18 to volunteer in a museum, just because of the 'fragile items and equipment I'd be required to use'! So the kitchen is quite a high-risk, fast-moving environment and they might want more mature volunteers. But call them; you never know.

can 15 year olds be allowed to voleneier as chefs in a non profit kitchen

You could look at setting this up as a Young Enterprise / Student Enterprise project. Be aware though that you would probably then be competing with the school canteen.

Probably best to talk with school staff first, to see how the idea might fit in with the curriculum and other strategic school activities. You shouldn't have any problem asking them a question like the above, and they may be in a position to extend the idea, in order to enable the project to contribute longer term funds to the school.